M. A. Quraishi Interdisciplinary Research Center for Advanced Materials King Fahd University of Petroleum and Minerals Dhahran Saudi Arabia
Taiwo W. Quadri Department of Chemistry School of Chemical and Physical Sciences and Material Science Innovation & Modelling (MaSIM) Research Focus Area Faculty of Natural and Agricultural Sciences North‐West University Mmabatho, South Africa
Chandrabhan Verma Interdisciplinary Research Center for Advanced Materials King Fahd University of Petroleum and Minerals Dhahran Saudi Arabia
Dakeshwar Kumar Verma Department of Chemistry Government Digvijay Autonomous Postgraduate College Rajnandgaon Chhattisgarh India
Xue Yang School of Materials Science and Engineering East China Jiao Tong University Nanchang People’s Republic of China
Saman Zehra Corrosion Research Laboratory Department of Applied Chemistry Faculty of Engineering and Technology Aligarh Muslim University Aligarh Uttar Pradesh India
Renhui Zhang School of Materials Science and Engineering East China Jiao Tong University Nanchang People’s Republic of China
1 An Overview of Corrosion
Marziya Rizvi
Corrosion Research Laboratory, Department of Mechanical Engineering, Faculty of Engineering, Duzce University, Duzce, Turkey
1 Introduction
1.1 Basics About Corrosion
Corrosion can be scientifically defined in many ways. The term “corrode” is itself obtained from the Latin word “corrodere,” i.e. “to gnaw to pieces.” The National Association of Corrosion Engineers (NACE) has defined it: “Corrosion is a naturally occurring phenomenon commonly defined as the deterioration of a material (usually a metal) that results from a chemical or electrochemical reaction with its environment” [1]. International Standard Organization explains “corrosion” technically as the “Physio‐chemical interaction between a metal and its environment which results in changes in the properties of the metal and which may often lead to impairment of the function of the metal, the environment or the technical system of which these forms a part” [2]. The environment is basically all that present surrounding and in contact with the observed metal/material. The primary factors describing the environment are (i) physical state (gas/liquid/solid); (iii) chemical composition (constituents &concentrations); and (c) the temperature. The corroded metal has obtained a thermodynamic stability in changing to oxides, hydroxides, salts, and carbonates. As per law of entropy, metals post fabrication return to their lowest energy, or natural ore form. Naturally metals are found in their element form or as ores. A lot is incorporated to convert iron ore into steel in the steel factories (Figure 1.1).
Figure 1.1 Corrosion cycle of steel.
Corrosion is the just reverse of what is known as extractive metallurgy. That implies that the energy utilized to convert an ore into a pure metal is reversed on exposure to environment (oxygen and water). On the exposed metal, oxides, sulfates, and carbonates exist [3–4]. Corrosion science as a subject has been around for many years in the textbooks, and surely its relevance has increased now. Education of corrosion and corrosion mitigation makes the environment safer and more sustainable.
1.2 Economic and Social Aspect of Corrosion
The incurred monetary losses and negative effects on environment geared the current ad on‐going researches in the field of corrosion. To sum up the total monetary loss due to corrosion, cost studies have been carried out in several countries. The first significant work on cost of corrosion was presented as a report by Uhlig in 1949, estimating the annual cost of corrosion as US$5.5 billion [5]. However, comprehensively the first study on losses incurred due to corrosion was conducted in the United States in late 1970s. In the year 1978, US$70 billion were wasted, equivalent to approximately 5% of gross national product (GNP) of that year [6]. The US Federal Highway Administration (FHWA) published a breakthrough study back in 2002, estimating the direct corrosion cost associated with USA’s industrial sector. The study was conducted by NACE International initiated the study as part of Transportation Equity Act for the 21st Century (TEA‐21), having a Congress mandate. The estimated direct cost of corrosion annually is $276 billion, which implies GNP’s 3.1% [7]. This estimation is solely inclusive of the direct costs pertaining to maintenance. Other expenditures after production loss, negative environmental effect, disrupted transports, fatalities, and injuries were computed to be as much as the direct costs. Similarly, some countries conducted corrosion cost studies. These countries were Australia, United Kingdom, Japan, Germany, Kuwait, Finland, India, China, and Sweden. It was inferred that annual corrosion costs was 1–5% of the national GNPs. The recently published material relates the global economic losses due to corrosion, summed up by NACE International in 2016 as $2.5 trillion, which is 3.5% of global GDP [8–10]. The Central Electrochemical Research Institute calculated the cost of corrosion in India by NBS input/output economic model for 2011–2012. The direct cost was US$26.1 billion or 2.4% GDP. The cost avoidable was US$9.3 billion or 35% direct cost of corrosion. The indirect cost was US$39.8 billion or 3.6% of IGDP [11]. NACE International according to the latest global studies estimated Indian cost of corrosion to be GDP’s 4.2% [12]. Beyond the cost of corrosion financially are the indirect costs like loss of opportunities and natural resources, potential hazards, etc. A project constructed using building material unable to withstand its environment for the estimated design life, the l resources are being needlessly consumed at later stages for maintenance and repair. Wasting the already depleting natural resources is a direct opposition to the increasing emphasis and demand for sustainable development in order to safeguard for future generations. Along with the wastage of natural resources, weak constructed structures pose threat to lives and well‐being. Huge safety concerns have been established in regards with the accidents that might happen in case of corroding structures. A single pipeline that fails, a bridge that collapses, a derailed train compartment due to corroded track, or other accidents is one among numerous that cause enormous indirect losses and huge public outcry. According to the market sector considered, the indirect losses might make up to 5–10 times the direct loss.
1.3 The Corrosion Mechanism
Corrosion occurs by formation of an electrochemical/corrosion cell (Figure 1.2).
This particular electrochemical cell comprises of five parts.
1 Anodic zones
2 Cathodic zones
3 Electrical contact between these zones
4 An electrolyte
5 A cathodic reactant
Inside this electrochemical cell, electrons depart from anodic to cathodic sites. The charged particles, ions, move across the conducting solution to balance the electrons flow. Anions (from cathodic reactions) move toward the anode and cations (from the anode itself) drift toward the cathode. Resultantly, anode corrodes and the cathode does not. There also exists a voltage/potential difference amidst anode and cathode. Numerous discrete micro cells develop on the metal surfaces, due to the constitutional phase difference, from stress variations, coatings, and